Synthesis of indolizines starting from pyrylium salts

β-N-Pyridinium acetaldehydes with alkyl substituents in the 2 and 6 positions of the pyridinium ring, obtained from the corresponding pyrylium salts, cyclise in alkaline medium to new indolizines. This high-yield reaction sequence is optimal for indolizines unsubstituted in the five-membered ring which are difficultly accessible by other methods.     

π-Aromatic complexes of metal carbonyls in the pyrylium salt series

By the reaction of lithium derivatives of cyclopentadienylmagnesiumtricarbonyl, cyclopentadienylrheniumtricarbonyl, and benzenechromiumtricarbonyl with 2,6-disubstituted pyrylium salts the corresponding 4H-pyrans have been synthesized, and the oxidative dehydration of these has given pyrylium cations containing the stated organometallic groups in position 4. It has been shown that the -complexes obtained readily exchange the oxygen of the pyrylium ring for other heteroatoms with the formation of heterocyclic compounds with metallocarbonyl substituents.Translated from Khimiya Geterosiklicheskikh Soedinenii, No. 5, pp. 593–597, May, 1985.     

Electronic absorption spectra of pyrylium and benzodihydrochromenylium salts

The electronic absorption spectra of benzodihydrochromenylium, tetrahydrochromenylium, and dichloropyrylium salts were studied for the first time. It was noticed that intramolecular charge transfer takes place mainly between the substituent at position 4 of the pyrylium ring and the π-system of the cation as a whole, while the bathochromic shift depends substantially on the geometry of the molecule. It was shown that the chlorine atoms have an effect on the form of the spectra when they are introduced into the ring of the pyrylium cation and into the aryl substituents. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1152–1159, August, 2008.     

Synthesis of pyrylium salts and pyridines containing heterocyclic substituents

A method of synthesizing pyrylium salts with heterocyclic substituents in the ring, has been investigated. The synthesis was carried out in two stages: alkaline condensation of aromatic and heterocyclic aldehydes with methyl ketones to give 1, 5-diketones, followed by cyclization to pyrylium salts by treatment with triphenylmethyl perchlorate. Pyridines containing heterocyclic substituents were obtained by treating the pyrylium salts with ammonia.     

Mercuration of Salts of 2- and 4-Methyl-substituted Heterocyclic Cations: A Quantum-Chemical Study

The deprotonation energies (H _r) of salts of 2- and 4-methyl-substituted pyridinium, pyrylium, quinolinium, and indolinium salts were evaluated by AM1 calculations. These data allow prediction of the mercuration pathway in reactions of these compounds with mercury salts. The structural factors affecting H _r and the main trends in variation of the geometric and electronic structures of the compounds upon their deprotonation in the course of mercuration were analyzed.     

Cyclopropyl-substituted pyrylium salts

The previously unknown 2,4,6-trisubstituted pyrylium salts 1-4 , carrying cyclopropyl and methyl or phenyl substituents in the same molecule, and 5-8 , substituted with isopropyl groups instead of cyclopropyl, were synthesized as perchlorates. The electronic spectra and the C-13 nmr spectra of the two groups of compounds were compared. A cyclopropyl group has a batochromic effect on the electronic spectrum roughly half that exerted by a phenyl; replacement of an alkyl by a cyclopropyl shifts the highest wavelength absorption band by about 20 nm. Presence of phenyl substituents reduces the batochromic effects of cyclopropyl substituents. The effects of both cyclopropyl and phenyl substituents on the electronic spectra are smaller for pyrylium than for tropylium. The nmr signals for all the ring carbons are shifted upfield upon replacement of isopropyl by cyclopropyl; in particular, the effect of substituents in position 2 upon the chemical shift of C(4) indicates that the electron-releasing effect varies in the series alkyl < phenyl < cyclopropyl, in agreement with the findings for 2,6-disubstituted pyrylium salts. The difference between the chemical shifts for the methine and methylene carbons of the three-membered ring is a function of the electron demand of the cationic heterocycle.     

Influence of the Structure of Steroid Hormones on Their Association with Cyclodextrins: A High-Performance Liquid Chromatography Study

The association constants of fourteen steroid hormones with - and -cyclodextrin were measured in methanol-water (20 : 80 v/v) at 35 °C using the chromatographic Hummel-Dreyer method. It was found that the greatest influence on the association constants is the structural features of ring A of these compounds but the substituents of ring D also alter the complex stability to an appreciable degree. The measured association constants were considerably greater than the corresponding values measured previously in the medium containing more methanol (45 instead of 20%).     

Preparation of pyridinium ylids, 1,4-dihydropyridines,and indolizines from γ-nitrophenyl- and γ-nitrobenzyl-pyridines

The transformations of N-phenacyl(p-nitrophenacyl, benzyl)-2,5-dimethyl-4-nitrophenyl (nitrobenzyl, benzyl)pyridinium bromides under the influence of potassium carbonate solution were studied. Stable pyridinium ylids were obtained in the case of -phenylpyridines that contain a nitro group in the benzene ring and in the case of -benzylpyridines with an N-nitrosubstituted phenacyl group. The conclusion that electron-acceptor substituents have a stabilizing effect on the stability of the ylids was confirmed. Under these conditions -nitrobenzyl derivatives are converted to substituted 1,4-dihydropyridines. The positions at which deprotonation of the starting quaternary pyridinium salts occurs and the formation of 1,4- and 1,2-dihydropyridines were established by PMR spectroscopy. The corresponding pyridinium salts were converted to a new group of indolizines containing a p-nitrophenyl (p-nitrobenzyl) substituent in the 2 or 7 position by the Chichibabin method. It was established that substituted dihydropyridines are converted to indolizines; ideas that confirm the scheme of the previously proposed mechanism for the formation of indolizines through a step involving ylids are expressed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 384–389, March, 1979.     

Ring transformations of heterocyclic compounds. X. A simple method for the conversion of methyl substituted pyridinium salts into 2,4,6-triarylphenyl derivatives: The first (thio)pyrylium ring transformations with heterocyclic anhydrobases as carbon nucleophiles

The synthesis of 2,4,6-triarylphenylpyridinium perchlorates 3 from methyl substituted derivatives 2 by a 2,6-[C₅+C] ring transformation of 2,4,6-triaryl(thio)pyrylium salts 1/4 in the presence of triethylamine/acetic acid in ethanol is reported. Spectroscopic data of the pyridinium perchlorates 3 and their formation via anhydrobases of the salts 2 are discussed.     

Condensation of acetals of aromatic β-keto aldehydes with ketones and phenols

Pyrylium salts with a free (active) position and different kinds of substituents in the, positions of the pyrylium ring were obtained by the reaction of acetals of aroylacetaldehydes with ketones and phenols.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1163–1165, September, 1972.     

1-Methyl-2(3,4)-(1-vinylpyrrol-2-yl)pyridinium iodides: some structural features revealed by 1H and 13C NMR spectroscopy

The reactions of 2-, 3-, and 4-(1-vinylpyrrol-2-yl)pyridines with methyl iodide afford the corresponding quaternary salts. Analysis of their ¹H and ¹³C NMR spectra showed that the quaternization of the nitrogen atom considerably enhances the -acceptor effect of the pyridine ring on the pyrrole ring and on the vinyl group. 1-Methyl-2-(1-vinylpyrrol-2-yl)pyridinium iodide contains no weak intramolecular C--H...N hydrogen bond present in the starting compound.     

Synthesis of functionally substituted benzo[c]pyrylium salts

Benzo[c]pyrylium salts that contain an acetyl, cyano, or ethoxycarbonyl group in the 4 position of the pyrylium ring were synthesized by the reaction of 3-(3,4-dimethoxyphenyl)pentane-2,4-dione and -(3,4-dimethoxyphenyl)acetoacetonitrile and ethyl -(3,4-dimethoxyphenyl)acetoacetate, as well as ethyl -(3,4-dimethoxyphenyl)benzoylacetate, with acyl perchlorates. It is shown that -(3,4-dimethoxyphenyl)acetoacetonitrile ethyleneketal is converted to 3-amino-4-acetylbenzo(c)pyrylium salts under these conditions.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 465–470, April, 1990.     

Β-Chloro-Β-ferrocenylacrylaldehyde and its application in the synthesis of pyrylium and pyridine derivatives of ferrocene

-Chloro--ferrocenylacrylaldehyde, to which an s-cis configuration was assigned on the basis of the PMR spectral data, was synthesized from acetylferrocene by the Vilsmeier-Haack reaction. 2, 3, 6-Trisubstituted pyrylium salts with a ferrocenyl substituent in the 6 position were obtained by condensation of this aldehyde with -dicarbonyl compounds. The pyrylium salts were converted to the corresponding pyridines by the action of ammonium acetate in acetic acid. On the basis of the structures of the pyridines it was established that the aldehyde carbon atom initially attacks the -dicarbonyl compound with subsequent closing of the -unsubstituted pyrylium ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 599–602, May, 1977.     

The pyrylation of aromatic and heterocyclic compounds

Pyrylium salts having no substituents in position 4 react with aromatic and heteroaromatic compounds forming 4-aryl- and 4-heterylpyrylium derivatives. The reaction takes place through the stage of the formation of a pyran which, with an excess of the initial pyrylium salt, splits out a hydride ion, aromatizing into a trisubstituted pyrylium cation.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 6, pp. 733–738, June, 1970.     

Reaction of 2,4,6-trimethyl- and 2,4,6-triphenylpyrylium perchlorates with heterocyclic amines

2,4,6-Triphenylpyrylium perchlorate reacts with most heterocyclic amines in dimethylformamide to give quaternary pyridinium salts. 2,4,6-Trimethylpyrylium perchlorate forms similar products only up to a certain limit of the basicity of the amine, below which a proton is transferred from the-methyl group of the pyrylium salt to the pyridine nitrogen atom of the heteroring to give the perchlorate of the starting heterocycle. The residual 2,6-dimethyl--methylenepyran is polymerized to a hexamer.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1461–1467, November, 1974.     

Polymers by the reaction of bis(pyrylium salts) with diamines: A novel approach to ionene polymers

The following reactions of pyrylium salts with amines are described: (1)bis(pyrylium salts) with amines; (2) diamines with pyrylium salts; and (3) bis(pyrylium salts) with diamines. Both (1) and (2) give bis(pyridinium salts) in high yields, and (3) gives the corresponding polymers which are isolated and characterized. This procedure was applied to cationic bis(pyrylium salts) to give cationic dimers and polymers, and further to zwitterionic bis(pyrylium salts) to yield the corresponding zwitterionic dimers and polymers.     

Direct synthesis of molecular self-complexes in the indole series

A method for the alkylation of 3-unsubstituted indoles by means of 1-(-haloalkyl)-pyridinium salts via the Friedel-Crafts reaction with the aid of complex catalysts, viz., complexes of zinc, tin, and titanium chlorides with pyridine, was developed. On the basis of a study of the electronic spectra of the resulting 1-(3-indolyl-alkyl)pyridinium salts it was shown that they are molecular self-complexes. The stabilities of the molecular self-complexes were investigated as a function of the length of the alkyl chain and the character of the substituents in the indole ring.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1222–1226, September, 1980.     

Synthesis of pyrylium salts by condensation of benzalacetophenone with aliphatic carbonyl compounds

The acid condensation of chalcone with aliphatic ketones, aldehydes, and -dicarbonyl compounds was studied for the first time. Tri- and tetrasubstituted pyrylium salts, including compounds containing functional substituents, were obtained.Translated from Khimiya Geterotsiklicheskih Soedinenii, No. 7, pp. 883–885, July, 1972.     

2‐(Azulen‐1‐yl)‐4,6‐diphenyl substituted six‐membered heteroaromatics

2‐(Azulen‐1‐yl)‐4,6‐diphenyl substituted pyranylium salts, pyridinium salts and pyridines were efficiently synthesized and the new obtained compounds were completely characterized. Comparative structural analysis between these compounds and their corresponding isomers that contain the azulen‐1‐yl moiety in the 4‐position of the heterocycle, were carried out. These studies are based on calculated dihedral angles formed between central heterocycle and the aromatic substituents and on the obtained electronic and NMR spectra. Due to the restriction in the rotation around azulenyl‐pyridinium bond produced by the quaternary nitrogen substituent, in the herein reported pyridinium salts, the substitution groups of the quaternary nitrogen atom are prochiral. This property leads to the non‐equivalence of gem‐protons or gem‐methyl groups of N‐substituents in the ¹H nmr spectra of the synthesized pyridinium salts.     

4-(Azulen-1-yl) six-membered heteroaromatics substituted in 2- and 6- positions with 2-(2-furyl)vinyl, 2-(2-thienyl)vinyl or 2-(3-thienyl)vinyl moieties

The synthesis of pyrylium and pyridinium salts and pyridines with azulene-1-yl moieties in position 4 and two 2-heteroarylvinyl groups in positions 2 and 6 was accomplished. The pyrylium salts were obtained starting from pyranones and pyridines could be prepared from these salts by treating them with ammonium acetate. The general procedures for the synthesis of pyridinium salts, which occur with good results in less delocalized electronic systems, do not take place when applied to the above obtained pyrylium salts. Therefore, as starting material 4-(azulen-1-yl)-1-(n-butyl)-2,6-dimethylpyridinium perchlorate was used, which was condensed with heteroarylcarboxaldehydes. These compounds were completely characterized and some of their spectra were discussed. Their interaction with some metal ions was revealed, observing an affinity better than in the case of simple azulenepyridines. In the last part of the paper are presented redox potentials for several pyrylium salts and pyridines in comparison with those of the nonvinylogated derivatives.